近50年我国西部地区气象要素的变化特征

利用1951-2000年全国194站地面观测资料和高空观测资料,对近50年我国西部地区的气候变化特征进行分析。结果表明:从20世纪70年代开始,我国西部地区年平均气温呈上升趋势,其中河套区和新疆区气温上升最为明显,其次为青藏高原区和河西区,西南区气温增幅最不明显,地表温度变化与气温的变化基本同步,但地温变化要比气温变化更加剧烈一些。西南区的地温从70年代中期开始回升,但始终未达到50年代初期的水平,因此从线性变化上表现为下降趋势。西部地区除了河套区外,其他4个区的年平均降水量均增加,增加最明显的是新疆区和青藏高原区。我国整个西部地区年平均总云量和低云量均呈线性减少趋势,减少最明显的是西南区和河套区。在辐射变化上,我国西部总辐射呈减少趋势,青藏高原区减少最多;西南区的散射辐射呈增加趋势,其他4个区减少,其中新疆区和青藏高原区散射辐射减幅明显。散射辐射的大小与天空中云量和气溶胶含量的多少成正比,西南区散射辐射呈增加趋势,而总云量和低云量呈下降趋势,可以推测是气溶胶含量增加导致了散射辐射的增加。

Characteristics of the Climate Change in West China in Recent 50 Years

Using the surface observational data and upper air data from 1951 to 2000 at 194 stations in China, the inter-annual and inter-decadal characteristics of climate in West China are analyzed. The results show that in the middle of 1970s, an evident climate sudden change happens to yearly average surface temperature,air temperature, precipitation, total cloud amount, low cloud amount and solar radiation. There is a rising trend of the annual mean temperature in West China. The most evident warming occurs in Hetao and Xin-jiang regions; in Tibet and Hexi regions warming is also evident, and in Southwest China the warming trend is less evident. The surface temperature changes in the same trend of the air temperature, and its variation is more significant. Particularly, the surface temperature in West China is getting higher since the middle of the 1970s, but it doesn't reach the level of that in 1950s, therefore shows a dropping trend in linear from 1951 to 2000. Annual mean precipitation takes on a rising trend all the regions in West China except for Hetao region, and the largest increase of rainfall occurs in Xinjiang and Tibet regions. Both the annual mean and season mean rainfall increases significantly in Xinjiang and Tibet regions, and the annual mean precipitation in 1990s increases 50% than that in 1950s. The precipitation in Xinjiang region keeps increasing in every season particularly in winter. Actually the precipitation is nearly zero in winter before 1978(except 1950s), and it begins to grow after that. The total cloudiness and the low cloudiness decrease linearly in West China in recent 50 years. The decreasing trends of annual mean low cloudiness are ob-served in all the areas, with the most remarkable decreasing rate in Hetao region and Southwest China, es-pecially in Hetao region where the rate is-1.7%/10 a. In Xinjiang region the cloudiness hasn't decreased much. The total radiation drops over the west regions, particularly in Tibet region. The change of solar direct radiation in the whole areas in West China is similar with that of total radiation. The southwest re-gion experiences an increasing trend in solar diffuse radiation, while a dropping trend in the other four are-as and the most evident decreasing occurs in Xinjiang and Tibet regions. The cloud amount and aerosol consistency have a close connection with solar diffuse radiation. In Southwest China, the solar diffuse radi-ation decreases as the cloud amount increases, so it's guessed that the decreasing of solar diffuse radiation is caused by the increasing of aerosol consistency.